Spring-type brake actuators are commonly used with air brake systems on wheeled vehicles such as trucks. A typical brake actuator, such as that illustrated in U.S. Pat. No. 3,796,138, issued Mar. 12, 1974, includes two separate actuator components, a service brake actuator assembly and an emergency brake actuator assembly.
The service brake actuator assembly applies the brakes of the vehicle through a push rod in response to air pressure delivered against a flexible diaphragm of the service actuator during the normal course of driving. In the emergency brake actuator assembly, a powerful compression spring in one portion of the emergency actuator chamber stores sufficient energy to apply the brakes. Air pressure in another portion of the emergency actuator chamber acts on another flexible diaphragm to compress the emergency actuator spring and maintain it in its brake-released position. When the air pressure is exhausted from the chamber, either under the control of the vehicle operator or due to the failure of the brake air system, the emergency actuator spring acts on the diaphragm and another push rod to actuate the service brake assembly and apply the brakes.
In the instant invention, it is desirable to maintain the emergency actuator spring chamber at atmospheric pressure so that the emergency diaphragm is met with minimum resistance as it moves into its brake-releasing position. This is accomplished by providing breather holes or openings in the spring chamber housing so that the chamber communicates directly with the outside air environment.
The use of such breather holes are known in the art. However, breather holes in a typical brake actuator create problems when the actuator is employed in an air environment of a wheeled vehicle that is commonly contaminated with dust, dirt, and other foreign matter. Each time the emergency brake actuator is engaged, contaminant-laden air is drawn into the emergency spring chamber through the breather holes. In addition, even when the emergency actuator is not being operated, foreign matter floating in the air may settle and enter the spring chamber through the breather holes, primarily those located in the upper portion of the spring chamber housing.
Depending upon the orientation of the actuator, the dust and dirt particles that enter the spring chamber will tend to settle under the force of gravity to the lowermost portion of the chamber, thus, leaving foreign matter to collect in the chamber. This accumulation of contaminants interferes with moving parts and, thus, hinders the performance of the brake actuator and shortens its useful life.